In today's competitive electronics marketplace, there is a demand for higher frequency computer components while consumers demand smaller packaging. These requirements have lead to much higher temperatures within the electronic package, requiring more cooling. Higher frequency computer components are also generating more electromagnetic interference or EMI in addition to the heat which, if not properly shielded, can interfere with other electronic equipment by way of radiation or conduction. Consequently, electronic manufacturers often face a design trade-off between cooling the package and shielding for EMI, since EMI radiation typically escapes through air holes commonly used for cooling purposes. It should efficiently be noted that radiations generated by electronic packages can include electromagnetic energy of wavelengths along various points of the spectrum such as radio frequency interference. As used herein, the term electromagnetic interference (EMI) refers to interfering electromagnetic energy of any wavelength.
Printed circuit boards used in various types of electronic equipment are typically mounted within a housing structure. During operation of the circuit board, EMI radiation is generated within the board, emanates therefrom, and must be substantially prevented from escaping outwardly through the housing structure. One solution to the above problem is to provide the housing with the necessary EMI radiation shield by coating the interior of the housing with a metallic material which is brought into contact with a grounding portion of the electronic circuits, such as the ground plane of the circuit board disposed within the housing. Other types of EMI shields positioned around the circuit board may be alternatively used. For instance it has been realized in the art that a foil shield, placed around the electronic circuitry and connected to ground would reduce EMI radiations. Typically aluminum or copper is used for such shields. However, such aluminum and copper foil shields, while somewhat effective, have proven to be costly to manufacturers. Moreover, none of the above solutions facilitate air circulation or improve cooling capabilities of the system.
In order to allow air circulation while reducing EMI, arrays of small flat holes have been used to shield against EMI, but the holes had to be so small that dust and lint would easily collect and clog the holes. In another solution, stacked plates of holes arranged into an array have been used, but the weight and cost of this solution make it unattractive. Yet another solution known in the art uses screen meshes, but this solution creates a high impedance air flow and presents a great risk of lint and dust build-up. Honeycomb vents have also been used for the same purpose, but the cost is prohibitive.
Accordingly, it is an object of the present invention to attenuate EMI radiation entering or leaving electronic packages to an acceptable level. It is a further object of the invention to produce an EMI radiation shielding device which allows for low impedance airflow through the package for cooling purposes. It is a further object of the invention to lower the cost compared to traditional EMI solutions. It is a still further object to reduce problems related to lint and dust collection around cooling holes.